1. Field of the Invention
The invention relates to optical communications systems, and parallel optic transceivers used in high throughput fiber optic communications links in local and wide area networks and storage networks, and in particular to fiber optic cables with integral transceivers mounted at each end for coupling to an electrical connector on an information system unit.
2. Description of the Related Art
Communications networks have experienced dramatic growth in data transmission traffic in recent years due to worldwide Internet access, e-mail, and e-commerce. As Internet usage grows to include transmission of larger data files, including content such as full motion video on-demand (including HDTV), multi-channel high quality audio, online video conferencing, image transfer, and other broadband applications, the delivery of such data will place a greater demand on available bandwidth. The bulk of this traffic is already routed through the optical networking infrastructure used by local and long distance carriers, as well as Internet service providers. Since optical fiber offers substantially greater bandwidth capacity, is less error prone, and is easier to administer than conventional copper wire technologies, it is not surprising to see increased deployment of optical fiber in data centers, storage area networks, and enterprise computer networks for short range network unit to network unit interconnection.
Such increased deployment has created a demand for electrical and optical transceiver modules that enable data system units such as computers, storage units, routers, and similar devices to be optionally coupled by either an electrical cable or an optical fiber to provide a high speed, short reach (less than 100 meters) data link within the data center.
A variety of optical transceiver modules are known in the art to provide such interconnection that include an optical transmit portion that converts an electrical signal into a modulated light beam that is coupled to a first optical fiber, and a receive portion that receives a optical signal from a second optical fiber and converts it into an electrical signal, and similar implementations employ one fiber for both optical signals, traveling in opposite directions. The electrical signals are transferred in both directions over an electrical connectors that interface with the network unit using a standard electrical data link protocol, such as Infiniband.
The optical transmitter section of such transceiver modules includes one or more semiconductor lasers and an optical assembly to focus or direct the light from the lasers into an optical fiber or fibers, which in turn, is connected to a receptacle or connector on the transceiver to allow an external optical fiber to be connected thereto using a standard connector, such as SC, FC, LC, or ribbon fiber type MPO. The optical receive section includes an optical assembly to focus or direct the light from the optical fiber or fibers onto a photodetector or array, which in turn, is connected to an IC circuit on a circuit board.
Optical transceiver modules are therefore packaged in a number of standard form factors which are “hot pluggable” into a rack mounted line card network unit or the chassis of the data system unit. Standard form factors set forth in Multiple Source Agreements (MSAs) provide standardized dimensions and input/output interfaces that allow devices from different manufacturers to be used interchangeably. Some of the most popular MSAs include XENPAK (see www.xenpak.org), X2 (see www.X2 msa.org), SFF (“small form factor”), SFP (“small form factor pluggable”), XFP (“10 Gigabit Small Form Factor Pluggable”, see www.XFPMSA.org), and the QSFP (“Quad Small Form-factor Pluggable,” see www.QSFPMSA.org).
In addition to such pluggable modules, customers and users of such systems are increasingly interested in fiber optic cables which incorporate integral transceivers fixedly mounted on the ends of such cables such as described in U.S. patent application Ser. No. 10/965,984. In order to increase the number of interconnections or port density associated with the network unit, such as, for example in rack mounted line cards, switch boxes, cabling patch panels, wiring closets, and computer I/O interfaces, such transceivers should be able to couple to multiple parallel optical fibers, or ribbons, and utilize parallel electro-optical converters in the transceivers.
A typical parallel optical transceiver consists of a vertical cavity surface emitter laser (VCSEL) array, and a PIN diode array. A parallel optical ribbon can be inserted into the optical transceiver, coupling to the VCSEL array or the PIN diode array, and individual lane transmitter and receiver properties can be measured. In these measurements the light source, a VCSEL array is adjusted or programmed over temperature to maintain good operating characteristics. The purpose of such receiver side measurements is that the driving conditions (e.g. bias voltage and current) of the VCSELs (or any other lasers) need to be adjusted and set at the factory since their threshold and efficiency varies from device to device and also changes as a function of temperature.
In an integrated module/optical cable, the parallel ribbon fiber may be permanently attached to electrical-optical converters at both ends. Since the optical interface is not accessible on either end, the VCSEL performance can not be measured or characterized directly. An alternative method must be found to properly characterize the performance of VCSEL over temperature to ensure the performance of the communications link.